Third Fridays at the Bechtler are free from 5 - 9pm! With a bar in the lobby and a scavenger hunt around the museum (with prizes), we spent about an hour and a half exploring the galleries and completing our worksheet. It wasn't very crowded when we were there, but I think the later you stay in the evening the more crowded it gets.
The museum is beautiful to begin with, and I loved the Sam Francis and Andy Warhol exhibits that were going on at the time. We ended up winning 4 free passes to the museum, so I can't wait to go back!